Buggy code:
@ SuppressWarnings ( "serial" ) public class ImparteGUI extends JFrame implements ActionListener { private JTextField tfClaveProfesor ; private JTextField tfClaveCurso ; private JTextField tfGrupo ; private JTextField tfHorario ; private JButton bRegistrar ; private JButton bConsultarProfesor ; private JButton bConsultarCurso ; private JButton bConsultar ; private JTextArea taDatos ; public JPanel p1 ; public JPanel p2 ; private ImparteAD imparte = new ImparteAD ( ) ; public ImparteGUI ( ) { } public JPanel getPanel2 ( ) { } public void clearFields ( ) { } public void habilitarBotones ( boolean value ) { } private void mostrar ( String str ) { } public boolean notTokenizer ( String str ) { } private String consultar ( String elemento ) { } private String obtenerDatos ( ) { } private void print ( String str ) { if ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( str . equals ( "PROFESOR_VACIO" ) ) || ( str . equals ( "CURSO_VACIO" ) ) ) || ( str . equals ( "CLAVE_NO_ENCONTRADA" ) ) ) || ( str . equals ( "CAMPO_VACIO" ) ) ) || ( str . equals ( "TOKEN" ) ) ) || ( str . equals ( "NO_NUMERICO" ) ) ) || ( str . equals ( "NEGATIVO" ) ) ) || ( str . equals ( "CLAVE_VACIA" ) ) ) || ( str . equals ( "SEMESTRE_NO_REGISTRADO" ) ) ) || ( str . equals ( "CLAVE_DUPLICADA" ) ) ) || ( str . equals ( "CURSO_NO_REGISTRADO" ) ) ) || ( str . equals ( "DEPARTAMENTO_NO_ENCONTRADO" ) ) ) || ( str . equals ( "CLAVE_NO_REGISTRADA" ) ) ) || ( str . equals ( "CURSO_DUPLICADO" ) ) ) || ( str . equals ( "PROFESOR_NO_ENCONTRADO" ) ) ) || ( str . equals ( "CURSO_NO_ENCONTRADO" ) ) ) { if ( str . equals ( "PROFESOR_VACIO" ) ) taDatos . setText ( "El<seq2seq4repair_space>campo<seq2seq4repair_space>'Clave<seq2seq4repair_space>Profesor'<seq2seq4repair_space>se<seq2seq4repair_space>encuentra<seq2seq4repair_space>vacío." ) ; if ( str . equals ( "CURSO_VACIO" ) ) taDatos . setText ( "El<seq2seq4repair_space>campo<seq2seq4repair_space>'Clave<seq2seq4repair_space>Curso'<seq2seq4repair_space>se<seq2seq4repair_space>encuentra<seq2seq4repair_space>vacío." ) ; if ( str . equals ( "CLAVE_CURSO_NO_ENCONTRADA" ) ) taDatos . setText ( ( ( "La<seq2seq4repair_space>Clave<seq2seq4repair_space>del<seq2seq4repair_space>Curso<seq2seq4repair_space>'" + ( tfClaveCurso . getText ( ) ) ) + "'<seq2seq4repair_space>no<seq2seq4repair_space>se<seq2seq4repair_space>encontró<seq2seq4repair_space>en<seq2seq4repair_space>la<seq2seq4repair_space>base<seq2seq4repair_space>de<seq2seq4repair_space>datos." ) ) ; if ( str . equals ( "CLAVE_PROFESOR_NO_ENCONTRADA" ) ) taDatos . setText ( ( ( "La<seq2seq4repair_space>Clave<seq2seq4repair_space>del<seq2seq4repair_space>Profesor<seq2seq4repair_space>'" + ( tfClaveCurso . getText ( ) ) ) + "'<seq2seq4repair_space>no<seq2seq4repair_space>se<seq2seq4repair_space>encontró<seq2seq4repair_space>en<seq2seq4repair_space>la<seq2seq4repair_space>base<seq2seq4repair_space>de<seq2seq4repair_space>datos." ) ) ; if ( str . equals ( "CAMPO_VACIO" ) ) taDatos . setText ( "Todos<seq2seq4repair_space>los<seq2seq4repair_space>campos<seq2seq4repair_space>deben<seq2seq4repair_space>contener<seq2seq4repair_space>datos." ) ; if ( str . equals ( "TOKEN" ) ) taDatos . setText ( "Los<seq2seq4repair_space>datos<seq2seq4repair_space>que<seq2seq4repair_space>se<seq2seq4repair_space>capturan<seq2seq4repair_space>no<seq2seq4repair_space>pueden<seq2seq4repair_space>contener<seq2seq4repair_space>un<seq2seq4repair_space>'_'" ) ; if ( str . equals ( "CURSO_DUPLICADO" ) ) <START_BUG> taDatos . setText ( ( ( ( ( "Ya<seq2seq4repair_space>se<seq2seq4repair_space>tiene<seq2seq4repair_space>registrado<seq2seq4repair_space>el<seq2seq4repair_space>grupo<seq2seq4repair_space>'" + ( tfGrupo . getText ) ) + "'<seq2seq4repair_space>para<seq2seq4repair_space>el<seq2seq4repair_space>curso<seq2seq4repair_space>" ) + ( tfClaveCurso . getText ( ) ) ) + ".<seq2seq4repair_space>\nPor<seq2seq4repair_space>favor<seq2seq4repair_space>introduce<seq2seq4repair_space>un<seq2seq4repair_space>grupo<seq2seq4repair_space>o<seq2seq4repair_space>curso<seq2seq4repair_space>o<seq2seq4repair_space>distinto" ) ) ; <END_BUG> if ( str . equals ( "CURSO_NO_REGISTRADO" ) ) taDatos . setText ( ( ( ( ( "El<seq2seq4repair_space>Profesor<seq2seq4repair_space>'" + ( tfClaveProfesor . getText ( ) ) ) + "'<seq2seq4repair_space>o<seq2seq4repair_space>el<seq2seq4repair_space>curso<seq2seq4repair_space>'" ) + ( tfClaveCurso . getText ( ) ) ) + "\'<seq2seq4repair_space>no<seq2seq4repair_space>están<seq2seq4repair_space>registrados<seq2seq4repair_space>en<seq2seq4repair_space>la<seq2seq4repair_space>base<seq2seq4repair_space>de<seq2seq4repair_space>datos.\nPor<seq2seq4repair_space>favor<seq2seq4repair_space>introduce<seq2seq4repair_space>nuevos<seq2seq4repair_space>datos<seq2seq4repair_space>válidos." ) ) ; if ( str . equals ( "PROFESOR_NO_ENCONTRADO" ) ) taDatos . setText ( ( ( "No<seq2seq4repair_space>se<seq2seq4repair_space>tienen<seq2seq4repair_space>cursos<seq2seq4repair_space>registrados<seq2seq4repair_space>para<seq2seq4repair_space>el<seq2seq4repair_space>profesor<seq2seq4repair_space>'" + ( tfClaveProfesor . getText ( ) ) ) + "'." ) ) ; if ( ( str . equals ( "NEGATIVO" ) ) || ( str . equals ( "NO_NUMERICO" ) ) ) taDatos . setText ( "El<seq2seq4repair_space>campo<seq2seq4repair_space>del<seq2seq4repair_space>\'Grupo\'<seq2seq4repair_space>debe<seq2seq4repair_space>contener<seq2seq4repair_space>un<seq2seq4repair_space>número<seq2seq4repair_space>válido<seq2seq4repair_space>entero<seq2seq4repair_space>positivo.\nPor<seq2seq4repair_space>favor<seq2seq4repair_space>introduce<seq2seq4repair_space>un<seq2seq4repair_space>nuevo<seq2seq4repair_space>grupo<seq2seq4repair_space>válido." ) ; if ( str . equals ( "CURSO_NO_ENCONTRADO" ) ) taDatos . setText ( ( ( "No<seq2seq4repair_space>se<seq2seq4repair_space>tienen<seq2seq4repair_space>cursos<seq2seq4repair_space>registrados<seq2seq4repair_space>con<seq2seq4repair_space>la<seq2seq4repair_space>clave<seq2seq4repair_space>'" + ( tfClaveCurso . getText ( ) ) ) + "'." ) ) ; } else taDatos . setText ( str ) ; if ( str . equals ( "BD_VACIA" ) ) taDatos . setText ( "No<seq2seq4repair_space>se<seq2seq4repair_space>ha<seq2seq4repair_space>registrado<seq2seq4repair_space>ningún<seq2seq4repair_space>artículo<seq2seq4repair_space>hasta<seq2seq4repair_space>el<seq2seq4repair_space>momento." ) ; } public void actionPerformed ( ActionEvent e ) { } public static void main ( String [ ] args ) { } }

Fix:
taDatos . setText ( ( ( ( ( "Ya<seq2seq4repair_space>se<seq2seq4repair_space>tiene<seq2seq4repair_space>registrado<seq2seq4repair_space>el<seq2seq4repair_space>grupo<seq2seq4repair_space>'" + ( tfGrupo . getText ( ) ) ) + "'<seq2seq4repair_space>para<seq2seq4repair_space>el<seq2seq4repair_space>curso<seq2seq4repair_space>" ) + ( tfClaveCurso . getText ( ) ) ) + ".<seq2seq4repair_space>\nPor<seq2seq4repair_space>favor<seq2seq4repair_space>introduce<seq2seq4repair_space>un<seq2seq4repair_space>grupo<seq2seq4repair_space>o<seq2seq4repair_space>curso<seq2seq4repair_space>o<seq2seq4repair_space>distinto" ) ) ;